1. Field of the Invention
The present invention relates to a level measuring device, and more particularly to a level measuring device having a lens antenna and a horn antenna mounted inside the lens antenna to protect against damage arising from exposure to corrosive object to be measured and increase a bandwidth of a reflection coefficient.
2. Description of the Related Art
Currently, to measure a level of a material or a liquid, an ultrasonic level meter or a radar level meter is needed and is mounted on an inner wall of a container adjacent to a top edge of the container to measure a height of the material or the liquid, which is calculated by a time difference between the time when ultrasonic wave or radar wave is transmitted and the time when the ultrasonic wave or radar wave is received. As being generally more accurate than ultrasonic level meters for level measurement of material or liquid, the radar level meters have been gradually and extensively applied to all types of level measurement occasions.
The most common type of the radar level meter is frequency modulated continuous waves (FMCW) level meter calculating a distance between the radar level meter and an object to be measured with a time difference between a time upon transmitting electromagnetic wave and a time upon receiving the electromagnetic wave that is reflected by the object to be measured. In turn, a height or a level of the object to be measured can be calculated from the time difference.
With reference to FIG. 14, a conventional radar level meter 90 has a base 91, a horn antenna 92, multiple circuit boards 93, a signal transceiver 94 and a lens antenna 96. An upper portion of the base 91 is hollow. The horn antenna 92 is connected with a lower portion of the base 91. The circuit boards 93 are mounted inside the upper portion of the base 91. The signal transceiver 94 is mounted inside the lower portion of the base 91, is located above the horn antenna 92, is electrically connected to the circuit boards 93 through a coaxial cable 95, transmit signals out through the horn antenna 92, and receives reflected signals through the horn antenna 92, so as to enhance directivity and bandwidth of the signals. The lens antenna 96 is mounted on an opening of the horn antenna 92 to provide a sealing effect. Since the horn antenna 92 has better directivity, electromagnetic wave transceived by the conventional radar level meter 90 can be more concentrated and is advantageous in longer distance measurement. When the base 91 is mounted on an inner wall of a container, the horn antenna 92 and the lens antenna 96 are located inside the container and are subjected to the effect of the object to be measured, such as high temperature, high pressure or corrosion caused by acidic or alkaline matter due to the exposure to a liquid to be measured or gas evaporated from the liquid. Once the horn antenna 92 or the lens antenna 96 is damaged, the radar level meter 90 fails to do any level measurement.
The container is usually barrel-shaped or cylindrical. A top edge portion of the container is designed to be curved for higher pressure resistance. When the conventional radar level meter is mounted on the top edge portion, the horn antenna 92 and the lens antenna 96 are not perpendicular to the level of the object to be measured and there is a tilt angle existing between a common center line of the horn antenna 92 and the lens antenna 96 and a direction perpendicular to the level of the object to be measured. The actual level measurement is therefore inaccurate.